Deceleartion brake control



Nov. 14, 1950 A, $1. \NHLLHAMS DECELERATICN BRAKE ammo;

4 Sheets-Sheet 1 Filed May 9, 1949 m T m m AllisOrLRWilliamS. BY

ATTORNEYS Ndv. 14, 1950 A. R. WILLIAMS 2,529,985

DECELERATION BRAKE CONTROL Filed May 9, 1949 4 Sheets-Sheet 3 INVENTOR.Allison R. Williams.

ATTORNEYS Nov. 14, 1950 A. R. WILLIAMS 2,529,985

DECELERATION BRAKE CONTROL Filed May 9, 1949 4 SheetsSheet 4 167 I II I160 v INVENTOR.

I50 Alli-SOIL R.W,ill,z'nms.

ATTORNEYS Patented Nov. 14, 1950 ou'i'rao STATES PATENT foFFica-DECELERATION BRAKE ooN'rnoL Allison B. Williams, Washington, D. 0.

Application Mu 9, 1949, Serial No. 92,170

This invention relates to methods and sy tems for controlling rotatingbodies or bodies mounted on rotating elements as wheels, the presentapplication being a continuation-in-part of my application Serial No.620,377, now abandoned, filed October 4, 1945 for Braking Systems. Moreparticularly the present invention relates to the control of theacceleration or deceleration of a rotating body by reference of itsactual acceleration or deceleration to and comparison with theacceleration or deceleration of rotation existing when there is noslipping or to a corresponding acceleration or deceleration oftranslation. I

In the case of wheeled vehicles, the present invention relates to amethod and system for maintaining'constant rolling contact between thewheels of the vehicle and the surfaces with which they have contact.More particularly still the present invention relates to the provisionin a braking system of means for minimizing slippage between the wheelsof a vehicle and the surfaces with which-they have rolling contactfollowing application of the brakes.

The invention is exemplified by reference to its application to thebraking systems of railway vehicles, but it is to be expresslyunderstood that the invention is not restricted to such applications, asit is applicable to the braking systems of automotive vehicles and othervehicles, as well as to other rotating bodies such as the rolls inrolling mills, paper mills, and other mills, where it-is desired tocontrol relative accelerations or decelerations at the same magnitude orat some constant differential or to maintain a previously plannedpattern of differences. As applied to braking systems the invention maybe embodied in systems powered by any suitable source of energy, and tosystems of any suitable type ior developing or transmitting the brakingeffort, as pneumatic, hydraulic, electrical or mechanical system.

Present conventional braking systems fail to make proper allowance forthe fact that the coefficient of adhesion between a wheel and thesurface contacted thereby, may be, and often is, at any given instantquite different for the several wheels ofthe vehicle as well as beingdifferent at successive times and under different conv ditions. It istrue that, with so called equalized brakes, as in known air, hydraulic,or mechanical systems used on vehicles, the braking effectsv of all thewheels are equalized to a high degree of precision (without introducingunbalanced lateral forces) so long as the friction between 2. the wheeland its contacting surface is greater thanthe brake friction applied,that is, so long as there is no wheel slipping. However, as soon as thebrake friction force exceeds the friction force acting tangentially tothe wheel between any wheel and its contacting surface that wheel tendsto decelerate more rapidly than occurs while proper rolling contact ismaintained. This leads to wheel locking and sliding, causing the wheelsof a railway vehicle to slide on the rails, with resultant flat surfaceon portions of the treads, and causing an automotive vehicle to skid andswirl if the brakes are being continuously applied.

Taking the case of automotive brakes, even though equally applied, ifthe brakes on one side effectively decelerate the vehicle and are noteffective on the other side of the vehicle due to insuillcient surfacefriction between. the wheels and the road, there results an unbalancedcouple tending to turn the vehicle about its vertical axis. Thissituation frequently causes collisions with tragic consequences.

It is an object of this invention to provide a method and system whereinthe proper instant of release of the brakes and of re-establishing brakeapplication is determined automatically, so as to discontinue brakeapplication with the utmost promptness after slipping commences and toreapply the brakes with equal promptness after slipping ceases.

It has heretofore been proposed to provide braking systems withmechanism responsive to rotary inertia to effect an automatic release ofthe brakes after slippage starts and reapplication of the brakes uponreacceleration of the wheels. Devices of this character as heretoforeproposed, however, have not only been highly complex, but they have beenopen to the objection that they fail to respond accurately orconsistently after slipping starts under varying conditions because theydepend on a predetermined amount of angular deceleration or apredetermined lapse of time having first occurred. Such proposedprovisions not only fail to act instantaneously at the beginning ofslippage, but as they depend on certain assumed conditions, determinedexperimentally or empirically, their response is rarely, if ever,consistent with the actual conditions, because such assumed conditionswill seldom be duplicated exactly owing to the infinite variety ofconditions of friction that may exist when the brakes are applied.

Another object of this invention is to provide a method and system forautomatically releas- For any given speed of translation for a wheel ona vehicle there is a proportional angular velocity for that wheel ifthere is no slipping.

- terms of a comparison between two values, as

two electric signals, one of which is proportional to the truedeceleration of translation as the standard of reference and which isproportional to the deceleration in angular velocity of the wheel whentrue rolling, with no creeping or slippage of the wheel, is occurring,and the other of which is proportional to the actual angulardeceleration of the wheel (it being understood that these two signals,either or both, may be biased so that an expression KXiB would expresstheir form rather than Kx, a simple proportion) the difierential valueobtained from an analysis of these two values can be used to effectrelease of the brake when it reaches an amount as small as practicallypossible to actuate physical elements, but of necessity sufficient inmagnitude to actuate the selected means for controlling the operation ofthe brake.

For example, in fluid operated brakes, a solenoid under the control of arelay actuated by two magneto motive forces obtained as explained abovecan operate a valve associated with the brake at the slipping wheel torelease the pressure, thereby allowing the wheel to re-establishcomplete rolling contact before it loses any appreciable rotationalkinetic energy. This can be accomplished without disturbing the brakingon other wheels, except when it is desirable to release simultaneously abrake on the opposite side of the vehicle to maintain constant lateralstability. Hence this automatic control will momentarily release thebrake on the slipping wheel (and possibly one of the wheels on theopposite sides of the vehicle) and then promptly reapply the brake assoon as true rolling is re.- established so that the operator cancontinue to decelerate the vehicle under stable and properly equalizedconditions maintained automatically.

It is a further object of this invention to provide means of the typelast characterized which are highly efficient, of simple constructionbut strong and durable, and certain in operation.

Furthermore, in coaction with the mechanism for so effecting momentaryrelease of the brakes, mechanism may be provided so that the same meanswhich releases the brake will concurrently release friction sand or thelike, causing some of it to be applied on the surface in front of therolling wheel. This provision may also be made effective if slippingoccurs during acceleration of a wheel and it may be used independentlyof the brake system.

Another object of this invention is therefore to provide a brakingsystem as hereinbefore characterized with automatically operating means4 for increasing the friction between a wheel and its contacting surfacesimultaneously with the automatic release of a brake, i. e., at thebeginning of slipping of any wheel.

Other objects will appear as the description of this invention proceeds.

The invention is capable of receiving a variety of mechanicalexpressions only some of which are shown on the accompanying drawings.Therefore it is to be expressly understood that the drawings are forpurposes of illustration only and are not to be construed as adefinition of the limits of the invention, reference being had i to theappended claims for that purpose.

Referring to the drawings, wherein the same reference characters areused to designate corresponding parts in the several figures,

Fig. 1 is a somewhat diagrammatic view illustrating one embodiment of anaccelerometer usable in the present invention to determine actual rotarydeceleration;

Fig. 2 is a section On the line 22 of Fig. 1;

Figs. 3 and 4 are fragmentary views to illustrate details of the deviceshown in Figs. 1 and 2;

Fig. 5 illustrates one form of accelerometer that may be used fordetermining vehicle deceleration as a standard signal that isproportional to the true rotary deceleration when no slipping exists;

Figs. 6 and '7 show graphs to aid understanding of the principlesinvolved and the operation of the invention;

Fig. 8 is a somewhat schematic view illustrating an embodiment of theinvention as applied to railway brakes;

Fig. 9 is a fragmentary view of a sander that may be used in embodyingthe present invention; and

Fig. 10 illustrates a preferred device used for obtaining the signalproportional to vehicle deceleration as a standard of comparison, and apreferred device used for obtaining the signal proportional to actualrotary deceleration of a wheel, and shows schematically another way ofcombining the signals.

Referring first to the involved principles, whenever the tangentialforce at the surface of contact between a wheel and the surface on whichit is rolling becomes less than the tangential force due to the brakewhich is being applied, slipping begins. This process may be.progressive because, as wheel slipping increases, the friction betweenthe wheel and the surface of contact may become still less, while brakefriction becomes greater, thereby causing effects which follow in rapidsuccession with the result that the angular velocity of the wheelapproaches zero very rapidly. Fig. '7 illustrates the above actionAssume that at time H a brake is applied. Both the of a wheel rotatingat angular velocit vl.

vehicle and thewheel then decelerate as shown by the sloping line I0. Ifat 112, t2 slipping of the wheel begins, it loses velocity very rapidly,decelerating along line H at a greater rate until,

in a very short period of time, if the brake is not released, the wheelis locked at time t5 when 05 equals zero. The time for the wheel todecelerate until it reaches a velocity equal to zero may be readilycalcu1atedfor a railway wheel rotating at a rotary speed correspondingto a train speed contact surface conditions.

shown empirically that with a constant brake pressure applied to thebrake shoe during braking of a vehicle from a high speed to a stop, thecoeillclent of friction between the wheel and brake does-not remain at aconstant value durin the total deceleration-period of the vehicle andtherefore during the period of time when the brake is being applied.This condition similarly applies for different brake pressures, and ageneral tendency can be noted, to wit, that at low velocities thetendency .is for the value of the coeflicientof friction to begreaterthan at higher velocities. vehicle'is being braked to a stop, inorder to effect the shortest stopping time,'this variable friction hasto be taken into consideration. The forces to be balanced in order toeffect maximum braking are those at the brake shoe and at the rail. Asthese act in opposite directions on the wheel itself, the optimumcondition is to have them exactly equal. .Under this condition themaximum braking force is being applied to the vehicle and the wheel isnot slipping. In contemporary systems the braking pressure maintained onthe shoe is of a constant value, and with the antislip devicesheretofore proposed it is changed if the wheel begins to slip. It isapparent that the utmost efficiency is never reached, however, becausethe original pressure applied might not cause slipping at the'higherspeed, while at lower speeds this same application of pressure wouldcause the braking force to exceed the frictional force of the rail andslipping would occur. In other words, these prior systems of control ofnecessity are not flexible enough to take into effect a constantlyvarying function such as here exists. The present invention, as willmore fully appear hereinafter, provides a system of control thatautomatically takes this varying function into consideration, just as itdoes any other variable condition, such as may exist at the rail itself,thereby effecting superior braking effects because operation depends ona diflerential value and not on any variation in the causes effectingthe values involved.

As will be apparent from the foregoinganalysis of the principles, themethod and system of the present invention involve the use of acomparison of signals from two devices responsive to changes in speed,which devices will herein be characterized as accelerometers, whetherresponding to positive or negative acceleration, i. e., decelartion. Tocarry into effect the foregoing principles one of said accelerometersresponds to the translational decleration of the wheel or other rotatingbody in its'motion of translation and therefore to the angulardeceleration of the wheel in its motion of rotation which corresponds tothat value which exists as long as complete rolling contact is beingmaintained between the wheel and its contacting surface, while the otheraccelerometer is made to respond to the actual angular deceleration ofth wheel under the existing tread and These decelerations will berespectively herein referred to as the normal angular deceleration andthe actual angular deceleration. Signals, such as indications ofmagnetomotive force, from said two accelerometers are compared todetermine if there is any existing differential over and above any biasthat may be imposed when the values are equal, and upon the occurrenceof any such differential that may be used to actuate suitablecontrolling mechanism, such differential becomes effective to initiatethe controlling function. In this inven- This means that during the timea.

sources of energy or the mechanism may be biased in a predetermineddirection so that upon the occurrence of a differential of predeterminedamount the responding mechanism may be actuated although the magnitudeof the diflerential might not itself be sufllcient to effect actuation-of the responding mechanism with the desired or suillcient promptness.

Any suitable devices may be employed for producing signals as sources ofenergy respectively responsive to the normal angular deceleration andthe actual angular deceleration and it is to be understood that they maybe installed to respond to a differential at each wheel, or toappropriately selected wheels, or to suitable groupings of wheels.

Referring first to Figs. 1 to 4, inclusive, one suitable device has beenillustrated for producing a source of energy or signal corresponding tothe actual deceleration of a wheel and which may be associated with eachwheel or selected wheels of the truck of a railway vehicle. As hereshown, l5 designates the truck wheel of any suitable railway vehicle,said wheel being energy proportional to the actual rotationaldeceleration of the wheel, casing 20 being shown as attached to thejournal box by suitable bolts and screws 2|. While the signal generatingmechanism is here illustrated as mounted on the end of the axle, it isto be expressly understood that any other appropriate means for mountingthe signal generating mechanism in association with the axle may beused.

Casing 20 is preferably so constructed as to minimize the chance offoreign matter entering the same, and to this end the chamber 22 in saidcasing is completely sealed except for the passage through the wallthereof of theshaft to be described. Journaled in any suitable way inthe wall of the casing 20 is a shaft 23 which protrudes through theinner wall 24 of the casing 20 and is there provided with any suitablemeans for rotating the shaft 23 in synchronism with the axle I5. Asshown, a threaded bolt 25 is mounted in the end of the axle l6 and hasappropriate connection with a crank 26 secured in any suitable way onshaft 23, The shaft 23 not only has a suitable bearing 21 in the wall 24of the housing 20 but it is also provided with a suitable bearing 28 inthe opposite wall of said housing, here shown as in the form of adetachable cover section 29.

Secured to the shaft 23 in any suitable way, as by keying, are twowheel-like devices 3| and 32. Each of these wheel-like devices carriesaround the periphery thereof a plurality of symmetrically arrangedU-shaped permanent magnets 33, with the legs of said magnets facedinwardly as illustrated. Said wheel-like devices 3| and 32 are providedwith the same number of U-shaped magnets and therefore a symmetricalmagnetic field is set up in the air gap between the two sets of inwardlydirected magnets. Disposed in this air gap and mounted on the shaftaoaaeso 2: for rotation relatively thereto is a. c151; 34,]

here shown asprovided with pinion teeth 35 at its periphery althoughother provisions for moving the rectilinearly movable member to be devbe appropriately secured to the wall of the housing 20. Rack 36 is alsoprovided with teeth 4| at its face opposite that carrying the teeth 42,and mounted on a stub shaft 43 carriedby the bracket 40 is a pinion 44meshing with said teeth 4|. Also mounted on the bracket 40 for freerectilinear movement thereon is a second rack 45 having teeth in meshwith the teeth of pinion 44. Rack 45 may be supported from the bracketin any suitable way, being shown as having its edges grooved at 46 forcooperation with flanges 41 carried by supporting plates 48 alsoprojecting inwardly from the bracket 40. As illustrated, the racks 36and 45 are supported in like fashion for linear movement and as bothracks are in mesh with pinion 44 they will have equal and oppositemovement when rack 36 is driven from the disk 34. -.By equating themasses of the racks 35 and 45 the effect of inertia is substantiallycanceled out.

The magnetic field set up by the U-shaped magnets 33 rotating with thewheel-like devices 3| and 32 therefore rotates in synchronism with thewheel axle l6 and eddy currents are set up in the disk 34 such that themagnitude of these currents is proportional to the instantaneous valueof the velocity of the pole faces of the magnets with respect to thedisk. These currents in turn set up a flux which reacts with the fluxset up by the permanent magnets, and thereby a tendency to displace thedisk rotationally is set up which at each instant is proportional to thespeed of rotation of the rotating magnetic field and thereforeproportional to the speed of rotation of the axle l5. Any suitable meansmay be associated with the disk 34 or the parts associated therewith toimpose a progressive resistance to the displacement of said disk.

The torque so developed by the rotating disk 34 is transmitted from therack 35 through any appropriate element or elements 50 to arectilinearly movable coil actuating member disposed in the magneticfield of a suitable permanent magnet 52 mounted in any suitable way onthe wall of the casing 20. Interposed between the element 50 and the end53 of said magnet 52 is a coil spring 54 which is preferably connectedat its opposite extremities to the element 50 and the end 53 of themagnet so that it may act in tension as well as in compression dependingupon the direction in which the coil actuating member 5| is moved by therack 35.

Carried by the coil actuating member 5|, and mounted for rectilinearmovement along the axis of the magnet 52, is a coil 55, here shown asslidingly mounted in the hollow core of a suitable bearing member 56that may also be carried in any suitable way from the base of theU-shaped magnet 52. As illustrated in Fig. 2, the coil 55 is designed totake up a position at approximately the midpoint in the length of thearms of the tion of the movement of the rack 36, balances the r U-shapedmagnet 52 when the spring 54 is under neither tension nor compression.When the i5 is in rotation, however the rotating magnetic field producedbythcwhe glike ni'embers 3| and 32 exerts a torque on'the' di'sk' 34which is transmitted through the rack 35, the element 50 and therectilinearly movable coil actuating member 5| to displace the'coil 55along the axis of the U-shaped magnet 52 by an amount which is exactlyproportional to the instantaneous speed of rotation of the axle I5. Asthe coil. 55 may be moved from its neutral position in either direction,the foregoing displacement of the coil 55 is in proportion to theinstantaneous speed of rotation of the axle "5 whether the wheel I5 isgoing forward or backward, and the spring 54, by compression or tensiondepending upon the directorque so created on the rotating disk 34'.

As before noted, the coil 55 is mounted to travel along a line bisectingthe space between the poles of the permanent magnet 52. As is wellunderstood in the art, the magnetic field existing between the poles ofa U-shaped magnet varies in strength along the line bisecting the spacebetween the poles as a linear function of the distance from the base ofthe U-shaped magnet to approximately the plane of the pole faces. As theposition of the coil 55 along this equi-potential line between the legsof the magnet is, at any given instant, in correspondence with theinstantaneous velocity of the axle Hi, the rate of change of the coilfrom one position to another along said equi-potential line isproportional to acceleration or deceleration at all points in the line.Hence, owing to the linearity of the foregoing function, themagnetomotive force generated in the coil 55 by its rate of displacementalong said equi-potential line is the same for like increments ofdisplacement whether at a given period of time there is a givendeceleration of the axle from a high speed of the axle, say miles perhour, or a low speed of the axle, say

five miles per hour. In other words, for a constant value ofdeceleration the coil moves with constant velocity along'its path andthe velocity of its movement is proportional to the rate of change ofrotational velocity, or angular deceleration or acceleration, of thewheel irrespective of the speed of rotation of said wheel at the instantwhen deceleration or acceleration begins.

Accordingly, if a constant velocity is imparted to the coil 55 along itsline of travel a constant voltage will be induced in the coil for thelength of that travel. Thereby a voltage is generated in the coil 55which is proportional to the instantaneous deceleration or accelerationof the disk 34 and therefore the axle Hi. This is 11-- lustrated in Fig.6 showing a graph 50 plotted on deceleration in miles per hour persecond and voltage generated in volts. As the position of the coil atany instant is determined by the instaneous velocity of the disk, therate of change of position of the coil over a given period of time willbe proportional to the deceleration of the disk. In decelerating, thecoil moves over an indeterminate path the length of which is a functionof the maximum velocity obtained by the disk before deceleration began.The U-shaped magnet 52 is so constructed that the length of theavailable path of movement of the coil is sufficient to take intoconsideration the maximum velocity to which the axle I5 is likely toattain. But as will be apparent from the graph of Fig. 6, a givendeceleration will induce a predetermined voltage which will be the sameat whatever point in the length of the graph the deceleration begins.whether near one end of the graph ill or the other, so that the voltageinduced is always proportional to the actual deceleration of the wheell5. Thereby the voltage generated in coil 55, which may be takentherefrom bysuitable leads 6|, affords a signal or source of energywhose strength is exactly proportional to the actual deceleration of thewheel I! at whatever speed of rotation of said wheel the decelerationbegins.

A second accelerometer of any suitable construction is provided on thevehicle for the purpose of providing a signal which is proportional tothe deceleration of the vehicle in translation or normal angulardeceleration of the wheel, such as occurs during the time the wheel ofthe vehicle is in rolling contact with the track or roadbed and thebraking force is not of such a character that slipping of the wheeloccurs. Under these circumstances the normal deceleration and actualdeceleration are the same.

One suitable accelerometer for responding to normal angular decelerationis shown in- Fig. which produces a continuous electromotive force outputproportional to the deceleration of trans lation of the vehicle andhence to the normal deceleration of the wheel such as exists when onlytrue rolling contact is maintained with the track. As here illustrated,a cylindrical iron coil.

10 has a primary winding ll embedded concentrically in its innersurface, one half of said winding being wound clockwise from one end tothe center line of the core and the other half being wound anticlockwisefrom said center line to the opposite end of the core so as to providetwo equal but oppositely wound sections. Connected across the terminalsof this primary coil is an oscillator 12 (Fig. 8) in circuit with anysuitable battery 13 or any other suitable source of direct current oralternating current generated in any suitable way on the vehicle.concentrically disposed within the primary winding H interiorly of thecore 10 is a soft iron spool 14 which carries a secondary winding 15whose ends are shown as connected to like springs I6 and 11 that alsoact as electrical connections as well as function to hold the spoolnormally so that the center of the secondary winding on the spool isaligned with the plane of junction of the two sections of the aforesaidprimary coil, i. e., at the point where the winding changes fromclockwise to anticlockwise. The coils on the core and spool have a theappropriate length and number of windings so that the terminalmagnetomotive force existing on the secondary coil 1*5 when generated bymovement of the spool lengthwise of-the core will exactly equal themagnetomotive force derivable from the accelerometer which responds toactual deceleration, such as the device of Figs. 1 to 4, when both areresponding to the same deceleration. In other words, when the normal andactual decelerations are the same the sources of energy generated by thetwo accelerometers are balanced. Spool 14 is rigidly centered within theprimary coil H by shafts l8 and 19 which project in opposite directionsfrom a piston 80 disposed-in an oil cylinder 8| provided interiorly ofthespool 14, said shafts at their outer extremities being guided insuitable bearings 83 and 84. Piston 80 is provided with the aperture '82extending therethrough...

and as the chambers at opposite sides of said piston are filled withoil, the piston 80 functions as a dash-pot to damp out any suddendisplacement of the spool that is not the result of a. truedeceleration.

The spool I4 is normally held in its neutral position by the springs Itand 11 with its medial plane coincident with the radial plane ofjunction between the two halves of the primary coil 1| as beforeexplained. Upon a change of speed of translation of the vehicle ineither direction the spool 14 is displaced axially of theprimary coil IIin one direction or the other, depending on the direction of movement ofthe vehicle, and against the resilience of the springs I6 and 11 Thespool 14 being free as. a seismic element to take up a positiondepending on the force of deceleration or acceleration existing at thecore 10, the displacement of the spool 14 will be proportional to therate of deceleration, and as the flux linking the primary and secondarywindings will, on movement of the spool 14, cause an induced voltage incoil 15 which is proportional to the displacement of the spool, suchinduced voltage aifords a signal which may be used for comparison withthe signal derived from the accelerometer responsive to the actualdeceleration of the wheel. The induced electromotive force in secondary15 may be rectified by any suitable rectifier (Fig. 8), synchronizedwith the oscillator 12, before it is applied to the signal comparingmeans of the control system.

Referring now to Fig. 8, wherein accelerometers of the form illustratedin Figs. 1 to 5 have been shown, although as will hereinafter appear theaccelerometers of Fig. 10 are preferred, the truck wheels I5 areprovided with any suitable brake mechanism which may be actuated andreleased by the admission and exhaust of any suitable brakeoperatingfiuid in conformity with the principles of braking systems wellknown in the art, such as conventional brake levers and brake rigging(omitted for purposes of clarity) responsive to variations of pressurein a brake cylinder diagrammatically indicated at 9|. Fluid underpressure is supplied to and released from the brake cylinder under thecontrolof the operator of the car or train by any suitable type ofcontrol equipment, as pneumatic brake control equipment either of the'automatic or the straight air type. For purposes of illustration, asimple operator type of brake control equipment of the straight air typehas been shown, but it is to be expressly understood that 'any' othersuitable type of operator control equipment may be used.

As illustrated, train pipes 94 and 95 extend the length of each car andare connected through hose couplings 96 with successive cars in thetrain in a manner well understood inv the art. Train pipe 94, which willhereinafter be referred to as the supply pipe, is constantly charged toa predetermined pressure corresponding to the pressure in reservoir 91,hereinafter referred to as the main reservoir, and which is connected toI supply pipe 94 through a suitable connection 98. The fluid pressure inpipe 95, hereinafter referred to as the control pipe, is varied inaccordance with the desired degree of brake application by a manuallyoperated valve device 99 of the selflapping type which is of wellknownconstruction and therefore will be referred to summarily byreference to its functions.

Brake valve device 99 includes an operating handle I00 effective uponrotary movement to actuate a rotary shaft for controlling the. opera--tion of suitable supply and release valves. With he rake handle I00 inits normal or brake reasaaeeo 11 lease position, fluid"under pressure isreleased from the control pipe 95 to atmosphere by way of a branch pipeIOI leading to the valve device 99 and thence to an exhaust pipe I02.When the brake handle I is shifted out of its brake release positioninto a zone of application, fluid under pressure is supplied from thesupply pipe 94 to the control pipe 95 by way of a branch pipe I02connecting the supply pipe 94 through said valve device 99 to thecontrol pipe 95 via branch pipe I M The character of the valve device 99is such that the pressure of the fluid established in the control pipe95 is substantially proportional to the degree of displacement of thebrake handle I00 out of its brake release position. As is more or lessconventional, the branch pipes IOI and I03 may be provided with valvesso as to close said branch connections when it is desired to remove thevalve device 99 from one car and operate the brakes from a similar valvedevice in another car of the train. The brake control equipment as sofar described further includes a control valve I06, such as disclosedfor example in the patent to E. E. Hewitt, No. 2,096,491, and anelectromagnetically actuated valve I0'I for controlling communicationbetween the two portions of a branch pipe I08 leading from supply pipe95 to said control valve I06. As the details of construction andoperation of said control valve I06 are fully set forth in the aforesaidpatent, said valve will be only described summarily herein by referenceto its function.

Fluid supplied from the control pipe 95 through the branch pipe I 08 tothe control chamber of the control valve I06 is efiective to operate thelatter and efiect a supply of fluid at a corresponding pressure, or anydesired ratio of pressure to that in control pipe 95, to the brakecylinder 9I through pipe I09 from pipe IIO connecting supply pipe 94with the control valve I06. As the valve I 06 is, as before mentioned,of the selflapping type, the supply of fluid under pressure to the brakecylinder 9I is automatically lapped or cut oil when the pressure in thebrake cylinder corresponds to or has a predetermined ratio to thepressure in the control pipe 95 as supplied to the control chamber ofthe valve I06.

The electromagnetically actuated valve I0! is diagrammaticallyillustrated as comprising a casing II2 having a chamber II3 formedtherein in which is disposed a double seating valve II4. Valve H4 isbiased by a coil spring II5 into an upper seated position in engagementwith a valve seat II6 leading to an exhaust pipe 1. Valve member II4 maybe moved against the tension of the spring I I 5 by an electromagnet orsolenoid II8 to a position in which said valve member II4 engages asecond seat II9 which controls the communication between the chambers Iand I2I with which communicate the before mentioned portions of the pipeI08 leading from control pipe 95 to control valve I06. When valve memberH4 is actuated by coil II8 against the tension of spring II5, valvemember II4 engages seat II 9 to break the communication between supplypipe 95 and valve I06. In this position the chamber I2I is open toexhaust through seat II 6 andtherefore the right-hand portion of thepipe I08 as viewed in Fig. 8, and which is in communication with valveI06, is thereby exhausted to atmosphere through a relatively large portwhich assures the release of pressure in the control chamber of thevalve I06.

The coil II 8 is energized by theonerat on of a relay I23 includ ng twowindings I24 and I 5 wound differentially. Winding I25 as illustratedreceives the signal derived from the accelerometer responsive to actualangular deceleration, here shown as mounted on the axle of the wheel asin Figs. 1 to 4, while winding I 24 receives the signal proportional toactual deceleration derived from the accelerometer 10. The diflerence inexcitation arising from the difference in electromotive forces existingin coils I24 and I25 operates the relay switch I26 to close the circuitthrough the coil I I8, any suitable battery or other source of electricenergy I21 being connected in circuit with said coil and relay,whereupon the valve member H4 is operated as described against thetension of the spring II5 to exhaust the fluid pressure from the valveI06 and thereby release the pressure in the brake actuating cylinder 9|.

From the foregoing description it will now be apparent that a signal isapplied to the coil I25 which is proportional to the actual decelerationas determined by the operation of the accelerometer hereinabovedescribed in connection with Figs. 1 to 4. Similarly, a signal isapplied to the coiL-I24'which is proportional to the normal declerationof the wheel as reflected in the actual deceleration of the vehicle,remembering that the actual deceleration of the vehicle corresponds tothe normal deceleration of the wheel if the wheel by reason of itscontact with the track or other surface is decelerating only at thatrate corre-v sponding to the deceleration of the vehicle and thereforewithout slippage at the wheel. If the wheel begins to slip the actualrotational deceleration of the wheel increases to a value above that ofthe normal rotational deceleration of the wheel, whereby a differentialelectromotive force is imposed on the relay device I23 by the coils I24and I25, whereupon the relay switch I26 is closed to energize the coilH8. Energization of coil II8 moves valve member II 4 against the tensionof the spring I I5 to exhaust the control chamber of valve I06 toatmosphere as heretofore explained, whereby the pressure is thereforereleased at the brake cylinder 9|. Hence the braking pressure is at oncereleased on the occurrence of an actual rotary deceleration in excess ofthe normal rotary deceleration. As soon as slipping ceases, however, thenormal and actual rotational decelerations again become equal, nodifferential electromotive force exists at the relay device I23,

the relay switch I26 is opened, coil H8 is deenergized, and valve memberII4 returns under the action of its spring II5 to restore communicationbetween the control pipe 95 and the relay device I06. By the use of asuitable type 01 relay I23, premature actuation of the switch I26 beforerolling contact is re-established can be prevented.

The foregoing operation is diagrammatically illustrated in Fig. '7 withsome distortion of the graph to avoid confusion from closely spacedlines. The vehicle is assumed to be moving at velocity vI until at timetI the brake is applied.

At first deceleration proceeds along the line I0 until time and velocity02, t2 are reached. 11' the wheel now begins to slip the actual angulardeceleration of the wheel is shown by the line II until at time t3 theactual angular ve-' locity has dropped to 03. If, now, the brake isreleased the angular velocity of the wheel increases to normal angularvelocity which is reflected at 1:4, t4 on line I2, line l2 being of lessslope than line I0 on the assumption that the braking force whenslipping of the wheel occurs ed and; hength 'b "1$;?eP 1f a time, andsubsequent decelerationffollows'" the line 13 which" isf'parallel"toiline 'I It fwill' I be e s th ft l ie ssqm le iw am ccur'. whetherslipping Starts at "the" beginning of br king-enemy after rmed of" braking' when. because of j the change in coefficient of friction at thedifferent speedfcontinuation ofithe same brakepressuremay initiateslipping, vWhenever during the braking period slipping 4 is initiated.

In other ,words, the difference inslgnalsor sources of energy at therelay, device I23 eifects an immediate release of the brake, and then.just-as quickly as true rolling is re-established'theflbrake pressureis reapplied, whereby maximum eifectiveness of the brake system ismaintained, utilizlng to the fullest extent possible whatever frictionexists between the wheel and its contacting surface. I 1

While as' so far described one particular form of accelerometerresponsive to normal translational or normal angular deceleration andone particular form ofaccelerometer responsive to actual angulardeceleration have been'illustrated and described by way of exemplifyingthe broader principles and method of the present invention, otheraccelerometers for producin the signals to be compared may .be used.

'Infact the preferred accelerometer for obtaining a signal proportionalto the translational or normal angular deceleration is illustrated inFig. 10. 7 As hereshown, a device utilizing a principle similar to thatof the slide wire potentiomcter has :been illustrated as comprising acylindrical iron-core I30 provided with a. slide wire rheostat windingI3I composed of two halves, one half from its ends-to the midpoint andthe other half from. said midpoint to the opposite end of .the core soas to provide two equal sectlons. Disposed in the hollow interior ofcoil I3I isan inertia member I32 mountedon a rod I 33 which extendsslldably through the end members I34 of the core and is secured toclamps I35. {Like springs I35 and I 31 are interposed between saidcollars I38 and clamps I35. One of said springs may also constitute anelectrical connection from a contact element I39 carried by inertiamember I32 and the lead I40 of the signal circuit. The other lead I ofthe signal circuit is connected to a post I42 disposed at the plane ofjunction of the two halves of the winding I 3|. The halves of windingI3I are energized by batteries I43 connected to the center post I42 andthe opposite ends ofthe respective halves. I, I 'Ifhejsprings I 3 andI31, when the vehicle is not accelerating or deceleratinghold thecontact element I39 in its neutral position atj the junction of the twohalves of the coil I3I.. .Upon occurrence of acceleration ordeceleratiomhowever, inertia member I32 moves against the re sllience ofsaid springs by an'amount which. is exactly proportional to the trueacceleration or deceleration of thevehicle to which the core I30 isattached, whereupon contact element I39 producesin the external circuit140, I H an electromotive force as a source'of energy which may beutilized as a signal at the coil [24 in Fig. 8 in the'same manner asheretoforefexplained, in conjunction with use of a signal from the.accelerometer 0! Fig.5. I v any other suitable accelerometer responsivei gushes In place of the devicefshown i" .Fig fIor obtaining a] signalpropo'rtional'tof actual angular decelerationof the wheel axle itJispreife'r redto employ a device of the type disclosed in" the patent to'Serrell No'. 2,090,521, .gran'te'd "August 17,;1937'anddiagrammatically illustrats translational {acceleration anddeceleration f may be used. such as a pressure potentiometer deviceworking on the principle of a variable resistance responsive to'changeso'f pressure, for example,,as disclosed 'in the patent tojl larrison No.2,391,956,grantedJanuaryl,1946., J

s.*1."to4

ed .in Fig. '10. As here shown, a rotor I45 of {the squirrel cagetype'is driven from or synchronously with the axle of the caranalogously as the embodiment of Figs. 1 and 4. Associated with saidrotor are four poles I45, I41, I43 and .I43 disposed at 90 apart.Directcurrent is supplied from any suitable battery or other source I50to coils I52 and I54 on the opposed poles I48. and I49 throughcircuitconnectlons I51, I53 and I55. The other two poles1I45' and I41are provided with coils I56 and I51, respectively, connectedthroughleads I58, I59=and I50 so that a signal may be taken off from the leadsI53 and I50 which'constitute a pick-up circuit for a study of thequadrature vflux set up by the currents induced in the rotor bars bythe-movement of these bars inthe field set up by the direct currentapplied to coils I52 and I54 on poles I48 and I 49. The voltage inducedin these bars is proportional to the instantaneous velocity of rotation.and the current flows setting up the quadrature flux. This flux, as thevelocity changes from one value to another, as in deceleration, in turninduces a voltage proportional to the rate of change of this flux in thepick-up windings I55 and I51. Thev voltage induced in the latter istherefore proportional to the deceleration of the rotor I45, which inturn is proportional to the actual deceleration of the wheel axle. Inorder to eliminate the transient effects interjected by the electricalcharacteristics or constants of the copper current-carrying loop in therotor, the resistance of the rotor circuit may be increased and theinductance of that circuit decreased by-making the pick-up iron circuitincluding the coils I55 and I5! of greater reluctance. This latter maybe efl'ected by decreasing the cross sectional area of the flux' returnpath in the frame of the machine as well as by decreasing the crosssectionalarea of the poles I45 and I4! as illustrated. There- .bylinearity of response under the varying'speed's likely to be encounteredis obtained.

Any other suitable accelerometer responsive to actual acceleration anddeceleration may. be used, as for example a device working on theprinciple disclosed in the patent to 'Kolff No. 2,364,256, grantedDecember 5, 1944.

'As before noted, the present invention also contemplates the provisionof'means for -increasing'the frictional'contact between the wheel andits con acting surface. when slippage starts, referably simultaneously;with the release of the brake, although as will be apparent to thoseskilled in the art the device tobe describedmay be used if slippageoccurs during acceleration and it also may be operated independently. ofthe brake. Referring to Fig. 9, I62 is a container of any suitablecharacter mounted on the frame of the vehicle in any suitable way as bybracket elements I53. Container I62 is provided with an outlet I64controlled by a valve member I55 having a. port I68 and connected by rodto trated in Fig; 9. Upon actuation of the solenoid or other coilassociated with the rod I65 the valve I65 is moved to align its apertureI68 with the outlet I64 so that sand or other suitable frictionincreasing material will flow through the delivery conduit I69 forapplication to the periphery of the wheelor to the surface contacted bythe wheel immediately in front 01. the latter.

Fig. further illustrates a system wherein the voltages produced by thetwo accelerometers are opposed to provide a diflerential voltage whichis suitably amplified as by means of a thermionic valve to operate theelectromagnetic valve I01 J (Fig. 8) which controls the brake releasingand reapplying means. If preferred, the thermionic valve may replace therelay switch I26 of Fig. 8, or as shown in- Fig. 10 the amplifiedcurrent may be used to operate a less sensitive relay. As stated above,the voltage across the leads I59. I60 is proportional to the actualangular deceleration, and the voltage across the leads III), MI isproportional to the normal angular deceleration. These leads 'areconnected to the terminals I10 so that the two voltages produced by theaccelerometers are opposed to provide a differential voltage equal tothe vector sum of the two voltages. The differential voltage is appliedby leads IN to a thermionic amplifier I12 of any suitable type and thecurrent in the output circuit I13 of the amplifier energizes a suitablerelay I14 adapted to close a switch I15 in the circuit of the solenoidII8 of the electromagnetic valve It will therefore be perceived that bythe present invention a relatively simple and highly sensitive methodand system have been provided for releasing a brake and efiectingcontrol over the degree of brake application instantaneously afterslippage starts. In fact, the only limitation upon the promptness withwhich the brake control is instituted is imposed by the inertia effectsof such movable parts as exist in the mechanical systems and the timeresponse characteristic in the electromagnetic systems. As amplifiersmay be introduced into either or both circuits, either before or aftercombination of the two signals in order to attain control, a very smalldifference in the sources of energy arising from the difference betweenthe actual rotational velocity of the wheel with respect to its velocityof translation will result in the brake being released before theangular momentum of the wheel has been materially decreased. A methodand system have thus been provided for comparing the normal angulardeceleration with the actual angular deceleration which obviates theinaccuracy, as well as the complexity, implicit in the use of theinertia-operative mechanisms heretofore proposed. Thus the comparison ofthe values derived from the normal and actual angular decelerations of awheel provides an accuracy of control that is independent of theexisting conditions as to friction, the occurrence of any particulardeceleration, the instantaneous speed at the instant when slippagestarts, any arbitrary lapse of time or amount of slip, and other factorsother than the existence of a decrease in the speed of the wheel belowthat which should exist for true rollin contact.

Use of the present invention also facilitates incorporation into thebraking system of additional useful features. For example, in anaccelerometer which is responsive to acceleration as well asdeceleration. no advantage has been taken in the system so far describedof the induced voltage due to acceleration. This induced voltage due toacceleration, when it has attained a predetermined value, can be used atany one wheel to release the-brakes at some or all of the remainingwheels, so that by going through the motion of applyin the brakes aspinning wheel may be locked to facilitate starting the vehicle if goodtraction exists at the other wheels.

The voltage induced in one or more of the accelerometers may also beused as a means of measuring speed. Speed being an integration ofacceleration, any suitable circuit may be associated with anaccelerometer for integrating the induced voltage-for example, a highresistance and capacity may be connected across the terminals of theaccelerometer and speed may be determined from the integrating effect ofsuch a system as measured across the capacity. Other useful auxiliarysystems facilitated by the use of the present invention will be apparentto those skilled in the art. l

While the embodiments of the invention illustrated on the accompanyingdrawings have been described with considerable particularity, it is tobe expressly understood that the invention is not limited thereto, asthesame is capable of receiving a variety of expressions'some of whichwill now readily suggest themselves to those skilled in the art.ticularly illustrated and described by reference to its use as a methodor system for controlling brake application on wheeled'vehicles 01' thetype adapted to run on tracks, 1. e., railways cars and trains, it willbe apparent to those skilled in the art that the invention is of equalapplicability to the control of brakes on automotive vehicles, such astrucks, tractors, automobiles, etc., wherein by use of the hereinbeforedescribed accelerometers or other comparable devices for generating andcomparin signals derived from and proportional to normal and actualangular deceleration of some or all of the wheels of the vehicle abrakingefiect on one or more of the wheels can be released to eliminateor minimize skidding and the like as soonas actual angular decelerationis predeterminately greater than normal angular deceleration for thethen existing translational deceleration. Also, as will be apparent tothose skilled in the art the invention is of even wider application thanto brake systems, as where as in rolling mills, paper mills, etc., othersystems of control are desired derivable from difierences in normal andactual rotational deceleration or acceleration of the rolls.

While certain accelerometers have been de-v scribed with considerabledetail, it is expressly understood that other accelerometers formeasuring either or both deceleration of translation and deceleration ofrotation can be used. Various other systems for comparing and utilizingthe sources of energy derived from thetwo accelerometers can beemployed, certain features. as the automatic sanding means, may be usedeither with the braking control or separately as desired, and variouschanges may be made in the details of construction,arrangementfproportion, size, etc., and elements illustrated may be re-While the invention has been parplacid by equlvalent elements. withoutdeparting from the spirit of the present invention. For defining thepresent invention reference is therefore to be had to the appendedclaims wherein the deceleration corresponding to true rolling, with noslippage. will be identified as the normal angular deceleration. forcomparison with the actual angular deceleration. by which is meant theactual deceleration of the wheel at any instant, the two being the'samewhen slippage is absent. but immediately providing a differential assoon as slippage starts, release of the brake being made to depend onlyon the existence of such a differential from whateve'r cause or causes,followed by reapplication of the brake upon disappearance of saiddifferential. It is also to be understood that said difierential may beconsidered zero as a practical matter, although not mathematically so,until a resultant diilferential of sufiicient magnitude in the sourcesof ener y is generated to close a relay. operate a thermionic valve,actuate a solenoid or other electromagnetic actuator, or otherwisecontrol the pressure of fluid in the brake cylinder for determining theapplication or release of the brake. or to actuate any other suitablemeans as an acceleration control or a deceleration control to controlrotary speed.

It will be understood that the term acceleration" in the followingclaims includes both positive accelerations and negative accelerationsor decelerations, and that the term accelerometer includes devicesresponding to negative accelerations or decelerations as well as thepositive accelerations.

What is claimed is:

1. In a system of the character described, in combination with a rotarymember and mechanism for controlling the speed of rotation thereof meansfor producing a source of energy proportional to the normal angulardeceleration of said member, means for producin a source of energyproportional to the actual deceleration of said member, means foropposing said sources of energy to obtain a force which is proportionalto the diflerence therebetweemand means operable by saidforce and actingto actuate said mechanism as soon as actual angular deceleration exceedsthe normal angular deceleration.

2. In a device of the character described. in combination with a rotarymember and mechanism for controlling the speed thereof, electrical meansfor producing an electromotive force which is proportional to the normalangular deceleration of said member, means for producing anelectromotive force which is proportional to the actual angulardeceleration of said member,

means for opposing said electromotive forces to obtain a forceproportional to the difference between said electromotive forces, andmeans responsive to said differential force and operatively connected tosaid mechanism for actuating the same.

3. In a braking system for wheeled vehicles, in combination with arotatable wheel and brake mechanism for retarding said wheel. means forreleasing and reapplying said brake mechanism, separate means forrespectively producing sources of energy that are proportional to thenormal angular deceleration and the actual angular deceleration of thewheel. meansfor opposing said sources of energy to produce adifferential force, and means responsive to said differential force foractuating said first named means.

asaaoas releasing and reapplying said brake mechanism.

means for supplying said wheel with friction-increasing material. anelectrical system including separate means for producing electromotiveforces that are respectively proportional to the normal-angulardeceleration and the actual angular deceleration of the wheel, means foropposing said electromotive forces to obtain a force which isproportional to the difference in values of said electromotive forces.and means operated by said last named force for actuating said releasingand reapplying means and said supplying means.

5. In a braking system for wheeled vehicles, in combination with arotatable wheel and brake mechanism for retardin said wheel, means forreleasing and reapp ying said brake mechanism. means for comparing theactual angular deceleration of the wheel with the normal angulardeceleration of said wheel, and means operable by a dlfi'erentialexisting in said comparing means for actuating said first named means.

6. In a braking system for wheeled vehicles, in combination with arotatable wheel and brake mechanism for retarding said wheel, means forreleasing and reapplying said brake mechanism, means for generating aforce that is proportional to the normal angular deceleration of thewheel. means for generating a force that is proportional to the actualangular deceleration of the wheel. means for creating a force that isproportional to the differential between said two first named forces andmeans operable by said last named means to actuate said first namedmeans.

7. In a braking system for wheeled vehicles. in combination with arotatable wheel and brake mechanism for retarding said wheel, means forreleasing and reapplying said brake mechanism, means for producingelectromotive forces that are always proportional to the actual angulardeceleration and the normal angular deceleration of the wheel, means foropposing said electromotive forces to obtain a force which isproportional to the difference between said first named electromotiveforces, and means operable by said last named force for actuating saidfirst named means.

8. In a braking system for wheeled vehicles, in combination with arotatable wheel and brake mechanism for retarding said wheel, means forreleasing and reapplying said brake mechanism, and means operable oninitiation of slippage of said wheel to actuate said first named meansand including means for producing a response that is proportional to theactual angular deceleration of the wheel, means for producing a responsethat is proportional to the normal angular deceleration of the wheel,and means for producing a response that is proportional to thedifference between said two responses and actuated as soon as the actualangular deceleration of said wheel exceeds the normal angulardeceleration thereof for operatin said first named means.

9. In a braking system for wheeled vehicles. in combination with arotatable wheel and brake mechanism for retarding said wheel, means forreleasing and reapplying said brake mechanism. and means operable oninitiation of slippage of said wheel to actuate said first named meansand including means responsive to the actual angular deceleration ofsaid wheel for generating an electromotive force proportional to saidactual angular deceleration. means responsive to the normal angulardeceleration of said wheel for generating an electromotive forceproportional to said normal angular deceleration, means for opposingsaid electromotive forces to obtain a diflerential upon the actualangular deceleration exceeding the normal angular deceleration of thewheel, and means responsive to said difierential for operating saidfirst named means.

10. In a braking system for wheeled vehicles, in combination with arotatable wheel and brake mechanism for retarding said wheel, means forreleasing and reapplyin said brake mechanism, and means operable oninitiation of slippage of said wheel to actuate said first named meansand including an accelerometer responsive to the actual angulardeceleration of said wheel, a second accelerometer responsive to thenormal angular deceleration of the wheel, a circuit into which saidaccelerometers are connected in opposition to provide a difierentialforce, and means actuated by said differential force for operating saidfirst named means.

11. In a braking system for wheeled vehicles, in combination with arotatable wheel and brake mechanism for retarding said wheel, means forreleasing and reapplying said brake mechanism, and means operable oninitiation of slippage of said wheel to actuate said first named meansand including an accelerometer responsive to the actual angulardeceleration of said wheel, a second accelerometer responsive to thenormal angular deceleration of the wheel, a circuit into which saidaccelerometers are connected in opposition to provide a difierentialforce, means energized by said differential force, and means actuated bysaid last named means for operating said first named means.

12. In a braking system for wheeled vehicles, in combination with arotatable wheel and brake mechanism for retarding said wheel, means forreleasing and reapplying said brake mechanism, and means operable oninitiation of slippage of said wheel to actuate said first named meansand including an accelerometer responsive to the actual angulardeceleration of said wheel, a second accelerometer responsive to thenormal angular deceleration of the vehicle, a system into which saidaccelerometers are connected in opposition to provide a forceproportional to the difierence between the actual and normaldeceleration of said wheel, means for supplying said wheel withfriction-increasing material, and means actuated by said force foroperating said first named means and said last named means.

13. In a braking system for wheeled vehicles, in combination with arotatable wheel and brake mechanism for retarding said wheel, means forreleasing and reapplying said brake mechanism, and means operable oninitiation of slippage of said wheel to actuate said first named meansand including an accelerometer responsive to the actual angulardeceleration of said wheel, a second accelerometer responsive to thenormal angular deceleration of the wheel, a circuit into which saidaccelerometers are connected in balanced opposition when the actual andnormal decelerations are the same, and means in said circuit actuated bya difference in the response of said accelerometers for operating saidfirst named means.

14. In a braking system for wheeled vehicles, in combination with arotatable wheel and brake mechanism for retarding said wheel, means forreleasing and reapplying said brake mechanism, means for supplyingfriction-increasing material to said wheel, means operable on initiationof slippage of said wheel to actuate both of said first named means andincluding means productive of a response proportional to the actualangular deceleration of the wheel, means productive of a responseproportional to the normal angular deceleration of the wheel, and meansresponsive to the responses of said two deceleration means and actuatedby a diilerence in the values thereof for operating both of said firstnamed means.

15. In a braking system for wheeled vehicles, in.

' combination with a rotatable wheel and brake wheel to actuate saidfirst named means and in--,

cluding an accelerometer responsive to the actual angular decelerationof said wheel, a second ac! celerometer responsive to the normal angulardeceleration of the wheel, a circuit into which said accelerometers areconnected in opposition and including means to provide a diiIerentialforce when the actual angular deceleration becomes greater than thenormal angular deceleration, and means actuated by said force foroperating said first named means.

16. In a braking system for wheeled vehicles, in combination with arotatable wheel and brake mechanism for retarding said wheel, means torreleasing and reapplying said brake mechanism, an electrical systemincluding separate current inducing means for respectively producingresponses that are proportional to changes in the normal angular andactual angular decelerations of the wheel, means for compounding theinduced currents to establish a difierential, and means operated by saiddifferential for actuating said first named means.

17. In a braking system for wheeled vehicles. in combination with arotatable wheel and brake mechanism for retarding said wheel, means forreleasing and reapplying said brake mechanism, means for inducinvoltages that are always proportional to the normal angular and theactual angular decelerations of the wheel, and means responsive to thevector sum oi! said voltages for actuating said first named means.

18. In a braking system for wheeled vehicles, in combination with arotatable wheel and brake mechanism for retarding said wheel, means forreleasing and reapplying said brake mechanism, means for inducingvoltages that are always proportional to the actual angular and thenormal angular decelerations of the wheel, an electrical circuit towhich said voltages are applied in opposition, a relay in said circuitactuated by a differential in said voltages, and operative connectionsbetween said relay and said first named means.

19. In a braking system for wheeled vehicles, in combination with arotatable wheel and brake mechanism for retarding said wheel, means forreleasing and reapplying said brake mechanism, and means operable oninitiation of slippage of said wheel to actuate said first named meansand including an accelerometer responsive to the actual angulardeceleration of said wheel, a second accelerometer responsive to thenormal angular deceleration of the wheel, a circuit into which saidaccelerometers are connected in opposition to provide a difierentialvoltage, means for amplifying said difi'erential voltage, and meansactuated by a predetermined difierential voltage for operating saidfirst named means.

.20. In a braking system for wheeled vehicles. I

in combination with a, rotatable wheel and brake mechanism for retardingsaid wheel, means for releasing and reapplying said brake mechanism, andmeans operable on initiation of slippage of said wheel to actuate saidfirst named means and including an accelerometer responsive to theactual angular deceleration of said wheel, a second accelerometerresponsive to the normal angular deceleration of the wheel, a circuitinto which said accelerometers are connected in opposition to provide adifferential voltage, and means actuated by a predetermined difierentialvoltage for operating said first named means, said last named meansincluding a thermionic tube and electrically operated means controlledby said tube for operating said first named means.

21. In a braking system for wheeled vehicles, in combination with arotatable wheel and brake mechanism for retarding said wheel, means forreleasing and reapplying said brake mechanism, and means operable oninitiation of slippage of said wheel to actuate said first named meansand including an accelerometer responsive to the actual angulardeceleration of said wheel, a second accelerometer responsive to thenormal angular deceleration of the wheel, a circuit into which saidaccelerometers are connected in opposition to provide a differentialvoltage, and means actuated by said differential voltage for operatingsaid first named means, said accelerometer responsive to normal angulardeceleration including a core 22 carrying a coil composed of a pair ofequal but oppositely wound sections, a spool carrying a winding andaxially movable in said core, and yieldable means for normally holdingthe midplane of the winding on said spool in alignment with the junction01' said first named coil sections but yieldable to permit axialdisplacement of said spool upon changes in'inertia of said spool.

ALLISON R. WILLIAMS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,019,314 Logan Oct. 29, 19352,038,146 Cook et al Apr. 21, 1936 2,132,914 Fitch Oct. 11, 19382,232,750 Wilson Feb. 25, 1941 2,232,752 Wilson Feb. 25, 1941 2,272,872Wilson Feb. 10, 1942 2,294,602 Hines Sept. 1, 1942 2,294,610 SorensenSept. 1, 1942 2,308,894 Place Jan. 19, 1943 2,321,059 Anderson June 8,1943 2,325,927 Wilbur Aug. 3, 1943 2,332,584 McCune Oct. 26, 19432,334,863 Canetta Nov. 23, 1943 2,393,031 Eksergian Jan. 15, 19462,435,310 Hines Feb. 3. 1948

